1. Field of the Invention
The present invention relates to an elliptical motion drive device for use in a step screen, and more particularly, to an elliptical motion drive device for use in a step screen in which a pair of eccentric wheels, having different eccentricities, are coupled to a single drive shaft to rotate upon receiving a force directly transmitted from the drive shaft, thereby enabling elliptical movement of a movable frame included in the step screen.
2. Description of the Related Art
In general, step screens are filtration apparatuses to convey and filter impurities contained in sewage flowing through pipes of sewage treatment plants or industrial wastewater treatment plants. To carry and capture impurities, the step screen comprises a plurality of lattice plates. The lattice plates consist of alternately arranged movable lattice plates and fixed lattice plates, each of which having a plurality of stepped teeth fixed at a predetermined angle. During operation, the movable lattice plates are lifted a predetermined distance every rotation to convey the captured impurities. The step screens are conventionally configured to convey and filter the impurities for post-treatment thereof without leakage of debris.
FIG. 1 is a side elevation view of a step screen according to the prior art. FIG. 2 is a front view of the step screen of FIG. 1. FIG. 3 is an exploded perspective view of an elliptical motion drive device for use in the step screen according to the prior art.
FIG. 4 is a partial sectional view of the elliptical motion drive device of FIG. 3. FIG. 5 is a schematic view illustrating the operation of the elliptical motion drive device according to the prior art.
Referring to FIGS. 1 to 5, the step screen of the prior art comprises movable lattice plates 7, which have a plurality of stepped teeth positioned at a sharp angle of more than 45° from the bottom of a sewage system. The movable lattice plates 7 are configured such that they cannot be tilted at a negative angle relative to a horizontal plane and thus are adapted to stably capture and convey impurities contained in sewage while performing elliptical motions. To drive the movable plates 7, the step screen is provided with an elliptical motion drive device. The elliptical motion drive device comprises a transverse eccentric cam 21 coupled at one side thereof to a drive shaft 3, that serves as a power transmission shaft and is rotatably connected to a reduction gear 2 of a drive motor 1. A transverse motion eccentric shaft 22 is coupled at one end thereof to the other end side of the transverse eccentric cam 21, so that a transverse eccentric bearing 24 coupled around the motion eccentric shaft 22 transversely moves along motion guiding rails 31 according to rotation of the traverse eccentric cam 21. The other end of the motion eccentric shaft 22 is coupled to a longitudinal eccentric cam 26, and a longitudinal motion eccentric shaft 27 is also coupled to the longitudinal eccentric cam 26, so that a longitudinal eccentric bearing 29 coupled around the longitudinal motion eccentric shaft 27 longitudinally moves along longitudinal motion guiding rails 32 according to the rotation of the transverse motion eccentric shaft 22.
With the elliptical motion drive device configured as stated above, according to the rotation of the drive shaft 3 of the drive motor 1 installed at the upper side of a fixed frame 4 included in the step screen, the transverse eccentric bearing 24 and the longitudinal eccentric bearing 29 simultaneously reciprocate in both transverse and longitudinal directions, respectively, thereby causing a movable frame 5 of the step screen that is connected with the steep toothed movable lattice plates 7 to elliptically move. Here, the elements realizing the elliptical motion of the movable frame 5 form an elliptical motion drive unit 19. The elliptical motion of the movable frame 5 connected to the elliptical motion device unit 19 is transmitted to the movable lattice plates 7 via links 9 and link arms 10, thereby causing the movable lattice plates 7 to perform regular elliptical motions in a longitudinal direction simultaneously with the movable frame 5. Thereby, the steep toothed movable lattice plates 7 are moved elliptically while being kept at a positive angle relative to the horizontal plane defined by the bottom of the sewage system, thereby effectively capturing impurities contained in the sewage.
In the case of the conventional elliptical motion drive device for use in the step screen as stated above, however, as a result of coupling both the drive shaft 3 and the transverse motion eccentric shaft 22 to the transverse eccentric cam 21 in parallel and as a result of coupling both the transverse motion eccentric shaft 22 and the longitudinal motion eccentric shaft 27 to the longitudinal motion eccentric cam 26 in parallel, the gap between the shafts is restricted, making it impossible to increase the diameter of the shafts in proportion to the increased load due to large-scale step screens.
Further, in spite of the fact that the rotating force of the drive shaft is transmitted to the transverse and longitudinal eccentric bearings by way of the plurality of eccentric shafts and the eccentric bearings must transmit the excessively high degree of rotating force, the conventional elliptical motion drive device takes the form of a cantilevered protruding arm in which the eccentric bearings are positioned far from a boss-coupling position of the drive shaft, resulting in a deteriorated structural integrity and durability.